This invention relates to a light exposure and illuminating device in which an outgoing light of an exposure light source is supplied to a site of light exposure for illuminating an object to be exposed to light.
Semiconductor or liquid crystal devices are fabricated by ultra-fine processing by photolithography. It is the lithographic device that performs the ultra-fine processing by photolithography. The lithographic device is employed widely because of its mass-producibility and low costs. In addition, the necessity for lithographic devices is felt more keenly with increase in demand for circuit integration.
In the lithographic device, it is the light exposure and illuminating device that illuminates a pattern to be recorded on a workpiece. As a light source for the light exposure and illuminating device, an i ray of a mercury lamp having a wavelength of 385 nm has been used.
The working limit of the lithographic device is inversely proportional to the wavelength of the outgoing light from a light source of a light exposure and illuminating device. In such case, it becomes necessary to maintain a depth of focus.
In any case, a variety of conditions are required of the light source of the light exposure and illuminating device. For example, the outgoing light of the slight source employed in the light exposure and illuminating device is required to have optical properties such as superior monochromaticity and incoherence. Since the outgoing light is of a short wavelength, it becomes possible to effect light exposure capable of coping with light exposure patterns of high resolution. For this reason, attempts are being made for reducing the wavelength of the outgoing light. In addition, the light source is required to be of high light output for achieving high throughput of the light exposure and illuminating device.
Among the light sources satisfying these conditions is an excimer laser. The excimer laser radiates a low-coherency laser light of multi-mode oscillation.
With the excimer laser, the laser radiating device itself is bulky in size. For actually generating the excimer laser, there is required an equipment taking up a large space such as cooling water equipment or a risky equipment handling toxic gases, thus entailing high costs in installation, management and maintenance. Since the spectral width of the excimer laser is reduced for avoiding chromatic aberration, speckles tend to be produced. In addition, the excimer laser is nonuniform in the spatial intensity distribution, such that, if such nonuniformity remains uncorrected, irregular light exposure results.
Among other light sources, there are a high-output solid laser, such as YAG, YVO.sub.4, Nd-glass laser, or a high-output gas laser, such as an argon ion laser, outgoing light beams of which are converted in wavelength by wavelength converting techniques employing non-linear optics. However, high outputs on the order of several watts cannot be obtained with the laser light beams reduced in wavelength by wavelength converting techniques. Consequently, such light source, if used for a light exposure and illuminating device, leads to prolonged light exposure time and hence is thought to be unfit for mass production of semiconductor devices.
In addition, the light source, reduced in wavelength by the wavelength converting techniques, presents circular Gaussian light intensity distribution. Since most of the semiconductor light exposure devices are of a system of repeating the registration and light exposure operations, the illuminated region is preferably rectangular in view of wafer utilization efficiency. However, since the above light source presents circular Gaussian light intensity distribution, part of light needs to be "kicked" if the light beam is directly used for light exposure, thus lowering the laser light utilization efficiency.
In a conventional illuminating system of a light exposure and illuminating device, employing an excimer laser, the light intensity distributions is uniformed with the aid of a fly-eye lens 55, as shown in FIG. 1. That is, the light exposure and illuminating device, employing the conventional excimer laser, is made up of an excimer laser 51, a beam expander 52, a mirror 53 having a piezoelectric device, a reflecting mirror 54, a fly-eye lens 55, a condenser lens 58, a light exposure mask 57 having a light exposure pattern formed thereon and an objective lens 58 for imaging the transmitted light on a wafer 59 in accordance with a light exposure pattern, with a view to uniforming the spatial intensity distribution of the excimer laser. However, such uniforming technique by the fly-eye lens 55 is designed to suit to characteristics of the excimer laser, such as the rectangular intensity distribution. Consequently, such uniforming technique, if applied to a light beam having intensity distribution exhibiting high rotation symmetry, such as Gaussian distribution, leads to poor intensity distribution uniforming effects and hence to poor light source utilization efficiency.